Method and apparatus for cardiac protection pacing

ABSTRACT

A pacing system delivers cardiac protection pacing to protect the heart from injuries associated with ischemic events. The pacing system detects an ischemic event and, in response, initiates one or more cardiac protection pacing sequences each including alternative pacing and non-pacing periods. In one embodiment, the pacing system initiates cardiac protection pacing sequences including at least one postconditioning sequence to protect the heart from a detected ischemic event and a plurality prophylactic preconditioning sequences to protect the heart from probable future ischemic events.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is related to co-pending, commonly assigned, U.S.patent application Ser. No. 11/030,575, entitled “INTERMITTENTAUGMENTATION PACING FOR CARDIOPROTECTIVE EFFECT,” filed on Jan. 6, 2005,U.S. patent application Ser. No. 11/113,828, entitled “METHOD ANDAPPARATUS FOR PACING DURING REVASCULARIZATION,” filed on Apr. 25, 2005,and U.S. patent application Ser. No. ______, entitled “METHOD ANDAPPARATUS FOR DELIVERING PACING PULSES USING A CORONARY STENT,” filed oneven date herewith (Attorney Docket No. 279.920US1), which are herebyincorporated by reference in their entirety.

TECHNICAL FIELD

This document relates generally to cardiac pacing systems andparticularly to a system for delivering pacing pulses to protect theheart from injuries associated with ischemic events.

BACKGROUND

The heart is the center of a person's circulatory system. It includes anelectro-mechanical system performing two major pumping functions. Theleft portions of the heart draw oxygenated blood from the lungs and pumpit to the organs of the body to provide the organs with their metabolicneeds for oxygen. The right portions of the heart draw deoxygenatedblood from the body organs and pump it to the lungs where the blood getsoxygenated. These pumping functions are resulted from contractions ofthe myocardium. In a normal heart, the sinoatrial node, the heart'snatural pacemaker, generates electrical impulses that propagate throughan electrical conduction system to various regions of the heart toexcite the myocardial tissues of these regions. Coordinated delays inthe propagations of the electrical impulses in a normal electricalconduction system cause the various portions of the heart to contract insynchrony to result in efficient pumping functions. A blocked orotherwise abnormal electrical conduction and/or deteriorated myocardialtissue cause dysynchronous contraction of the heart, resulting in poorhemodynamic performance, including a diminished blood supply to theheart and the rest of the body. The condition where the heart fails topump enough blood to meet the body's metabolic needs is known as heartfailure.

Myocardial infarction (MI) is the necrosis of portions of the myocardialtissue resulted from cardiac ischemia, a condition in which themyocardium is deprived of adequate oxygen and metabolite removal due toan interruption in blood supply caused by an occlusion of a blood vesselsuch as a coronary artery. The necrotic tissue, known as infarctedtissue, loses the contractile properties of the normal, healthymyocardial tissue. Consequently, the overall contractility of themyocardium is weakened, resulting in an impaired hemodynamicperformance. Following an MI, cardiac remodeling starts with expansionof the region of infarcted tissue and progresses to a chronic, globalexpansion in the size and change in the shape of the entire leftventricle. The consequences include a further impaired hemodynamicperformance and a significantly increased risk of developing heartfailure, as well as a risk of suffering recurrent MI.

Therefore, there is a need to protect the myocardium from injuriesassociated with ischemic events, including MI.

SUMMARY

A pacing system delivers cardiac protection pacing to protect the heartfrom injuries associated with ischemic events. The pacing system detectsan ischemic event and, in response, initiates one or more cardiacprotection pacing sequences each including alternative pacing andnon-pacing periods.

In one embodiment, a cardiac pacing system includes a sensing circuit,an ischemia detector, a pulse output circuit, and a control circuit. Thesensing circuit senses one or more signals indicative of an ischemicevent. The ischemia detector detects the ischemic event from the one ormore signals. The pulse output circuit delivers pacing pulses. Thecontrol circuit controls the delivery of the pacing pulses and includesa cardiac protection pacing sequence initiator and a cardiac protectionpacing timer. The cardiac protection pacing sequence initiator initiatesone or more cardiac protection pacing sequences in response to thedetection of the ischemic event. The one or more cardiac protectionpacing sequences each include alternating pacing and non-pacing periods.The pacing periods each have a pacing duration during which a pluralityof the pacing pulses is delivered. The non-pacing periods each have anon-pacing duration during which none of the pacing pulses is delivered.The cardiac protection pacing timer times the one or more cardiacprotection pacing sequences.

In one embodiment, a method for delivering the cardiac protection pacingis provided. One or more signals indicative of an ischemic event aresensed. The ischemic event is detected from the one or more signals. Oneor more cardiac protection pacing sequences are initiated in response tothe detection of the ischemic event. The one or more cardiac protectionpacing sequences each include alternating pacing and non-pacing periods.The pacing periods each have a pacing duration during which a pluralityof pacing pulses is delivered. The non-pacing periods each have anon-pacing duration during which no pacing pulse is delivered. Theplurality of pacing pulses is delivered during each of the pacingperiods.

This Summary is an overview of some of the teachings of the presentapplication and not intended to be an exclusive or exhaustive treatmentof the present subject matter. Further details about the present subjectmatter are found in the detailed description and appended claims. Otheraspects of the invention will be apparent to persons skilled in the artupon reading and understanding the following detailed description andviewing the drawings that form a part thereof. The scope of the presentinvention is defined by the appended claims and their legal equivalents.

BRIEF DESCRIPTION OF THE DRAWINGS

The drawings illustrate generally, by way of example, variousembodiments discussed in the present document. The drawings are forillustrative purposes only and may not be to scale.

FIG. 1 is an illustration of an embodiment of a cardiac rhythmmanagement (CRM) system including an implantable system and an externalsystem and portions of an environment in which the CRM system is used.

FIG. 2 is a block diagram illustrating an embodiment of portions of thecircuit of a cardiac pacing system of the implantable system.

FIG. 3 is a block diagram illustrating a specific embodiment of portionsof the circuit of the cardiac pacing system.

FIG. 4 is a block diagram illustrating an embodiment of portions ofcircuits of the implantable system and the external system.

FIG. 5 is a block diagram illustrating an embodiment of the externalsystem.

FIG. 6 is a flow chart illustrating an embodiment of a method fordelivering pacing pulses for cardiac protection.

FIG. 7 is a flow chart illustrating a specific embodiment of the methodfor delivering pacing pulses for cardiac protection.

DETAILED DESCRIPTION

In the following detailed description, reference is made to theaccompanying drawings which form a part hereof, and in which is shown byway of illustration specific embodiments in which the invention may bepracticed. These embodiments are described in sufficient detail toenable those skilled in the art to practice the invention, and it is tobe understood that the embodiments may be combined, or that otherembodiments may be utilized and that structural, logical and electricalchanges may be made without departing from the spirit and scope of thepresent invention. References to “an”, “one”, or “various” embodimentsin this disclosure are not necessarily to the same embodiment, and suchreferences contemplate more than one embodiment. The following detaileddescription provides examples, and the scope of the present invention isdefined by the appended claims and their legal equivalents.

This document discusses a pacing system including an implantable medicaldevice that delivers pacing pulses to protect the heart from injuriesassociated with ischemic events, including MI. The pacing pulses aredelivered to the heart to change the distribution of stress in themyocardium, thereby triggering the intrinsic myocardial protectivemechanism against ischemic damage to the myocardial tissue. In oneembodiment, the implantable medical device detects ischemic events. Inresponse to the detection of an ischemic event, a cardiac protectionpacing sequence is initiated to protect the heart from ischemic damagecaused by the detected ischemic event by delivering a pacingpostconditioning therapy. Then, additional cardiac protection pacingsequences are initiated to protect the heart from ischemic damage causedby potentially recurrent ischemic events by delivering a prophylacticpacing preconditioning therapy. The pacing postconditioning therapy andthe prophylactic pacing preconditioning therapy each include delivery ofone or more cardiac protection pacing sequences each includingalternating pacing and non-pacing periods. The pacing periods each havea pacing duration during which a plurality of pacing pulses isdelivered. The non-pacing periods each have a non-pacing duration duringwhich no pacing pulses is delivered. In other words, the pacingpostconditioning therapy and the prophylactic pacing preconditioningtherapy each include intermittent delivery of pacing pulses over apredetermined duration.

FIG. 1 is an illustration of an embodiment of a cardiac rhythmmanagement (CRM) system 100 and portions of an environment in whichsystem 100 is used. System 100 includes an implantable system 105, anexternal system 115, and a telemetry link 112 providing forcommunication between implantable system 105 and external system 115.

Implantable system 105 includes, among other things, implantable medicaldevice 110 and lead system 108. In various embodiments, implantablemedical device 110 is an implantable CRM device including one or more ofa pacemaker, a cardioverter/defibrillator, a cardiac resynchronizationtherapy (CRT) device, a cardiac remodeling control therapy (RCT) device,a neruostimulator, a drug delivery device or a drug delivery controller,and a biological therapy device. As illustrated in FIG. 1, implantablemedical device 110 is implanted in a body 102. In various embodiments,lead system 108 includes leads for sensing physiological signals anddelivering pacing pulses, cardioversion/defibrillation shocks,neurostimulation pulses, pharmaceutical agents, biological agents,and/or other types of energy or substance for treating cardiacdisorders. In one embodiment, lead system 108 includes one or morepacing-sensing leads each including at least one electrode placed in oron a heart 101 for sensing electrogram and/or delivering pacing pulses.In other embodiments, electrodes placed in body 102 but away from heart101 are used to sense physiological signals and deliver pacing pulses,cardioversion/defibrillation shocks, neurostimulation pulses,pharmaceutical agents, biological agents, and/or other types of energyor substance for treating cardiac disorders. In a specific embodiment,one or more electrodes are incorporated onto implantable medical device110 for subcutaneous placement.

Implantable medical device 110 includes a cardiac pacing system 120.Cardiac pacing system 120 is capable of delivering cardiac protectionpacing therapies through lead system 108. The delivery of a cardiacprotection pacing therapy is timed as a cardiac protection pacingsequence including alternating pacing and non-pacing periods. In oneembodiment, in addition to the cardiac protection pacing therapy,cardiac pacing system 120 also delivers one or more other cardiac pacingtherapies, such a bradycardia pacing therapy, CRT, and RCT. If anotherpacing therapy is being delivered when a cardiac protection pacingsequence is to be initiated, that pacing therapy is temporarilysuspended to allow the delivery of the cardiac protection pacing therapyand resumed upon completion of the cardiac protection pacing sequence.

External system 115 allows a user such as a physician or other caregiveror a patient to control the operation of implantable medical device 110and obtain information acquired by implantable medical device 110. Inone embodiment, external system 115 includes a programmer communicatingwith implantable medical device 110 bi-directionally via telemetry link112. In another embodiment, external system 115 is a patient managementsystem including an external device communicating with a remote devicethrough a telecommunication network. The external device is within thevicinity of implantable medical device 110 and communicates withimplantable medical device 110 bi-directionally via telemetry link 112.The remote device allows the user to monitor and treat a patient from adistant location. The patient monitoring system is further discussedbelow, with reference to FIG. 5.

Telemetry link 112 provides for data transmission from implantablemedical device 110 to external system 115. This includes, for example,transmitting real-time physiological data acquired by implantablemedical device 110, extracting physiological data acquired by and storedin implantable medical device 110, extracting therapy history datastored in implantable medical device 110, and extracting data indicatingan operational status of implantable medical device 110 (e.g., batterystatus and lead impedance). Telemetry link 112 also provides for datatransmission from external system 115 to implantable medical device 110.This includes, for example, programming implantable medical device 110to acquire physiological data, programming implantable medical device110 to perform at least one self-diagnostic test (such as for a deviceoperational status), and programming implantable medical device 110 todeliver at least one therapy.

FIG. 2 is a block diagram illustrating an embodiment of portions of thecircuit of a cardiac pacing system 220. Cardiac pacing system 220 is aspecific embodiment of cardiac pacing system 120 and includes a sensingcircuit 222, an ischemia detector 224, a pulse output circuit 226, and acontrol circuit 228. Sensing circuit 222 senses one or more signalsusing a plurality of electrodes and/or one or more sensors. The one ormore signals are indicative of ischemic events. Ischemia detector 224detects the ischemic events from the one or more signals. Pulse outputcircuit 226 delivers pacing pulses to heart 101. Control circuit 228controls the delivery of the pacing pulses based on the one or moresensed signals and/or in response to the detection of each ischemicevent. In various embodiments, cardiac pacing system 220 issubstantially contained in an implantable housing of implantable medicaldevice 110.

Control circuit 228 includes a cardiac protection pacing sequenceinitiator 230 and a cardiac protection pacing timer 232. Cardiacprotection pacing sequence initiator 230 initiates one or more cardiacprotection pacing sequences in response to the detection of eachischemic event. The one or more cardiac protection pacing sequences eachinclude alternating pacing and non-pacing periods. The pacing periodseach have a pacing duration during which a plurality of pacing pulse isdelivered. The non-pacing periods each have a non-pacing duration duringwhich no pacing pulse is delivered. Once a cardiac protection pacingsequence is initiated, cardiac protection pacing timer 232 times thatsequence. The one or more cardiac protection pacing sequences each havea sequence duration in a range of approximately 30 seconds to 1 hour.The pacing duration is in a range of approximately 5 seconds to 10minutes. The non-pacing duration is in a range of approximately 5seconds to 10 minutes.

FIG. 3 is a block diagram illustrating an embodiment of portions of thecircuit of a cardiac pacing system 320. Cardiac pacing system 320 is aspecific embodiment of cardiac pacing system 220 and includes sensingcircuit 222, ischemia detector 224, pulse output circuit 226, and acontrol circuit 328. Sensing circuit 222 senses the one or more signalsindicative of the ischemic events. Ischemia detector 224 detects theischemic events from the one or more signals. Pulse output circuit 226delivers the pacing pulses to heart 101. Control circuit 328 controlsthe delivery of the pacing pulses based on the one or more sensedsignals and/or in response to the detection of each ischemic event. Invarious embodiments, cardiac pacing system 320 is substantiallycontained in an implantable housing of implantable medical device 110.

Ischemia detector 224 includes an ischemia analyzer running an automaticischemia detection algorithm to detect the ischemic event from the oneor more signals. In one embodiment, ischemia detector 224 produces anischemia alert signal indicative of the detection of each ischemicevent. The ischemia signal is transmitted to external system 115 forproducing an alarm signal and/or a warning message for the patientand/or a physician or other caregiver.

In one embodiment, ischemia detector 224 detects the ischemic eventsfrom one or more cardiac signals. Sensing circuit 222 includes a cardiacsensing circuit. In a specific example, cardiac signals are sensed usinga wearable vest including embedded electrodes configured to sensesurface biopotential signals indicative of cardiac activities. Thesensed surface biopotential signals are transmitted to implantablemedical device 110 via telemetry. In another specific embodiment,ischemia detector 224 detects the ischemic events from one or morewireless electrocardiogram (ECG) signals. Sensing circuit 222 includes awireless ECG sensing circuit. A wireless ECG is a signal approximatingthe surface ECG and is acquired without using surface (skin contact)electrodes. An example of a circuit for sensing the wireless ECG isdiscussed in U.S. patent application Ser. No. 10/795,126, entitled“WIRELESS ECG IN IMPLANTABLE DEVICES,” filed on Mar. 5, 2004, assignedto Cardiac Pacemakers, Inc., which is incorporated by reference in itsentirety. An example of a wireless ECG-based ischemia detector isdiscussed in U.S. patent application Ser. No. 11/079,744, entitled“CARDIAC ACTIVATION SEQUENCE MONITORING FOR ISCHEMIA DETECTION,” filedon Mar. 14, 2005, assigned to Cardiac Pacemakers, Inc., which isincorporated by reference in its entirety. In another embodiment,ischemia detector 224 detects the ischemic events from one or moreelectrogram signals. Sensing circuit 222 includes an electrogram sensingcircuit. Examples of an electrogram-based ischemia detector arediscussed in U.S. Pat. No. 6,108, 577, entitled, “METHOD AND APPARATUSFOR DETECTING CHANGES IN ELECTROCARDIOGRAM SIGNALS,” and U.S. patentapplication Ser. No. 09/962,852, entitled “EVOKED RESPONSE SENSING FORISCHEMIA DETECTION,” filed on Sep. 25, 2001, both assigned to CardiacPacemakers, Inc., which are incorporated herein by reference in theirentirety.

In another embodiment, ischemia detector 224 detects the ischemic eventsfrom one or more impedance signals. Sensing circuit 222 includes animpedance sensing circuit to sense one or more impedance signals eachindicative of a cardiac impedance or a transthoracic impedance. Ischemiadetector 224 includes an electrical impedance based sensor using a lowcarrier frequency to detect the ischemic events from an electricalimpedance signal. Tissue electrical impedance has been shown to increasesignificantly during ischemia and decrease significantly after ischemia,as discussed in Dzwonczyk, et al. IEEE Trans. Biomed. Ens., 51(12):2206-09 (2004). The ischemia detector senses low frequency electricalimpedance signal between electrodes interposed in the heart, and detectsthe ischemia as abrupt changes in impedance (such as abrupt increases invalue).

In another embodiment, ischemia detector 224 detects the ischemic eventsfrom one or more signals indicative of heart sounds. Sensing circuit 222includes a heart sound sensing circuit. The heart sound sensing circuitsenses the one or more signals indicative of heart sounds using one ormore sensors such as accelerometers and/or microphones. Such sensors areincluded in implantable medical device 110 or incorporated into leadsystem 108. Ischemia detector 224 detects the ischemic event bydetecting predetermined type heart sounds, predetermined type heartsound components, predetermined type morphological characteristics ofheart sounds, or other characteristics of heart sounds indicative ofischemia.

In another embodiment, ischemia detector 224 detects the ischemic eventsfrom one or more pressure signals. Sensing circuit 222 includes apressure sensing circuit coupled to one or more pressure sensors. In aspecific embodiment, the pressure sensor is an implantable pressuresensor sensing a signal indicative of an intracardiac or intravascularpressure whose characteristics are indicative of ischemia.

In another embodiment, ischemia detector 224 detects the ischemic eventfrom one or more acceleration signals each indicative of regionalcardiac wall motion. Sensing circuit 222 includes a cardiac motionsensing circuit coupled to one or more accelerometers each incorporatedinto a portion of a lead positioned on or in the heart. The ischemiadetector detects ischemia as an abrupt decrease in the amplitude oflocal cardiac accelerations.

In another embodiment, ischemia detector 224 detects the ischemic eventfrom a heart rate variability (HRV) signal indicative of HRV. Sensingcircuit 222 includes an HRV sensing circuit 760 to sense the HRV andproduce the HRV signal, which is representative of an HRV parameter. HRVis the beat-to-beat variance in cardiac cycle length over a period oftime. The HRV parameter includes any parameter being a measure of theHRV, including any qualitative expression of the beat-to-beat variancein cardiac cycle length over a period of time. In a specific embodiment,the HRV parameter includes the ratio of Low-Frequency (LF) HRV toHigh-Frequency (HF) HRV (LF/HF ratio). The LF HRV includes components ofthe HRV having frequencies between about 0.04 Hz and 0.15 Hz. The HF HRVincludes components of the HRV having frequencies between about 0.15 Hzand 0.40 Hz. The ischemia detector detects ischemia when the LF/HF ratioexceeds a predetermined threshold. An example of an LF/HF ratio-basedischemia detector is discussed in U.S. patent application Ser. No.10/669,168, entitled “METHOD FOR ISCHEMIA DETECTION BY IMPLANTABLECARDIAC DEVICE,” filed on Sep. 23, 2003, assigned to Cardiac Pacemakers,Inc., which is incorporated by reference in its entirety.

Control circuit 328 is a specific embodiment of control circuit 228 andincludes a pacing mode switch 334, a pacing mode controller 336, acardiac protection pacing sequence initiator 330, and a cardiacprotection pacing timer 332. Control circuit 328 allows cardiac pacingsystem 320 to control the delivery of the cardiac protection pacingtherapy as well as other pacing therapies. This allows the function ofcardiac protection pacing to be included in an implantable medicaldevice that delivers pacing therapies on a long-term basis, such as fortreatment of bradycardia and heart failure. In various embodiments,cardiac protection pacing therapy includes a temporary pacing therapydelivered for one or more brief periods in response to the detection ofeach ischemia event, and the implantable medical device also delivers achronic pacing therapy such as a bradycardia pacing therapy, CRT, orRCT. In other embodiments, the cardiac protection pacing therapy is theonly pacing therapy delivered, or the cardiac protection pacing therapyis the only pacing therapy programmed to be delivered for at least acertain period of time.

Each pacing therapy is delivered by delivering pacing pulses inaccordance with a predetermined pacing mode. Pacing mode switch 334switches the pacing mode from a chronic pacing mode to a temporarypacing mode when a cardiac protection pacing sequence is initiated andto switch the pacing mode from the temporary pacing mode to the chronicpacing mode when the cardiac protection pacing sequence is completed.Pacing mode controller 336 controls the delivery of the pacing pulsesfrom pulse output circuit 226 according to the pacing mode as selectedby pacing mode switch 334. The temporary pacing mode refers to thepacing mode used in a cardiac protection pacing therapy, which is atemporary pacing therapy. The chronic pacing mode refers to the pacingmode used in a chronic pacing therapy such as a bradycardia pacingtherapy, CRT, or RCT. In one embodiment, the temporary pacing mode issubstantially different from the chronic pacing mode, such that thecardiac protection pacing therapy changes the distribution of stress inthe myocardium, thereby triggering the intrinsic myocardial protectivemechanism against ischemic damage to the myocardial tissue. Examples ofthe temporary pacing mode include VOO, VVI, VDD, and DDD modes,including their rate-responsive versions if applicable. In oneembodiment, the pacing rate is set to be about 20 pulses per minutehigher than the patient's intrinsic heart rate during the temporarypacing mode. In a specific embodiment, if the cardiac protection pacingtherapy is the only pacing therapy being delivered (in other words, thechronic pacing mode is a non-pacing mode), the temporary pacing mode isan atrial tracking pacing mode such as the VDD or DDD mode, includingtheir rate-responsive and multi-ventricular site versions. If thechronic pacing mode is an atrial tracking pacing mode such as the VDD orDDD mode, the temporary pacing mode is a VOO or VVI mode at with apacing rate higher than the patient's intrinsic heart rate or a VDD orDDD mode with substantially different pacing parameter such as a pacingrate, pacing sites, and/or atrioventricular pacing delays.

Cardiac protection pacing sequence initiator 330 is a specificembodiment of cardiac protection pacing sequence initiator 230 andinitiates one or more cardiac protection pacing sequences in response tothe detection of each ischemic event. In one embodiment, cardiacprotection pacing sequence initiator 330 also initiates one or morecardiac protection pacing sequences in response to one or more commandsissued by the user through external system 115. For example, following adiagnosis of vulnerable plaque indicative of a high risk for MI, aphysician applies a pacing preconditioning therapy by starting a cardiacprotection pacing sequence by issuing such a command. Cardiac protectionpacing timer 332 times the one or more cardiac protection pacingsequences including the alternating pacing and non-pacing periods.

In one embodiment, the one or more cardiac protection pacing sequencesinitiated in response to the detection of each ischemic event include atleast one postconditioning sequence and a plurality of prophylacticpreconditioning sequences. As illustrated in FIG. 3, cardiac protectionpacing sequence initiator 330 includes a postconditioning sequenceinitiator 338 and a preconditioning sequence initiator 340, and cardiacprotection pacing timer 332 includes a postconditioning timer 342 and apreconditioning timer 344.

Postconditioning sequence initiator 338 initiates the postconditioningsequence in response to the detection of an ischemic event. In oneembodiment, postconditioning sequence initiator 338 initiates thepostconditioning sequence when the end of the ischemic event isdetected. In one embodiment, the end of the ischemic event is detectedwhen the ischemic event is no longer detected by ischemia detector 224.In one embodiment, postconditioning sequence initiator 338 initiates thepostconditioning pacing sequence when a post-ischemia time intervalexpires. The post-ischemia time interval starts when the end of theischemic event is detected and is up to approximately 10 minutes, withapproximately 30 seconds being a specific example. In one embodiment,the post-ischemia time interval is chosen such that the postconditioningpacing sequence is initiated after the reperfusion phase following theischemic event has started. In another embodiment, postconditioningsequence initiator 338 initiates the postconditioning pacing sequence inresponse to one or more postconditioning commands issued by the user.

Preconditioning sequence initiator 340 initiates the prophylacticpreconditioning sequences, one at a time, after the end of the ischemicevent is detected and the postconditioning sequence is completed. In oneembodiment, preconditioning sequence initiator 340 initiates theprophylactic preconditioning pacing sequences on a periodic basis usinga predetermined period. The predetermined period is in a range ofapproximately 24 hours to 72 hours, with approximately 48 hours being aspecific example. In another embodiment, preconditioning sequenceinitiator 340 initiates the prophylactic preconditioning pacingsequences according to a programmed preconditioning schedule. In anotherembodiment, preconditioning sequence initiator 340 initiates theprophylactic preconditioning pacing sequences in response to one or morepreconditioning commands issued by the user.

Postconditioning timer 342 times the postconditioning sequence includingalternating postconditioning pacing and non-pacing periods. Thepostconditioning pacing periods each have a postconditioning pacingduration during which a plurality of pacing pulses is delivered. Thepostconditioning non-pacing periods each have a postconditioningnon-pacing duration during which no pacing pulse is delivered. Thepostconditioning sequence has a postconditioning sequence duration in arange of approximately 30 seconds to 1 hour, with approximately 10minutes being a specific example. The postconditioning pacing durationis in a range of approximately 5 seconds to 10 minutes, withapproximately 30 seconds being a specific example. The postconditioningnon-pacing duration is in a range of approximately 5 seconds to 10minutes, with approximately 30 seconds being a specific example.

Preconditioning timer 344 times the prophylactic preconditioning pacingsequences including alternating preconditioning pacing and non-pacingperiods. The preconditioning pacing periods each have a preconditioningpacing duration during which a plurality of pacing pulse is delivered.The preconditioning non-pacing periods each have a preconditioningnon-pacing duration during which no pacing pulse is delivered. Theprophylactic preconditioning pacing sequences each have apreconditioning sequence duration in a range of approximately 10 minutesto 1 hour, with approximately 40 minutes being a specific example. Thepreconditioning pacing duration is in a range of approximately 1 minuteto 30 minutes, with approximately 5 minutes being a specific example.The preconditioning non-pacing duration is in a range of approximately 1minute to 30 minutes, with approximately 5 minutes being a specificexample.

In one embodiment, control circuit 328 detects an arrhythmia andsuspends the one or more cardiac protection pacing sequences in responseto the detection of the arrhythmia. Control circuit 328 includes anarrhythmia detector to detect one or more predetermined types ofarrhythmia. In one embodiment, cardiac protection pacing sequenceinitiator 330 cancels, holds, or otherwise adjusts the timing of theinitiation of a cardiac protection pacing sequence in response to adetection of arrhythmia. In one embodiment, cardiac protection pacingtimer 332 terminates or suspends a cardiac protection pacing sequence inresponse to the detection of an arrhythmia that occurs during thecardiac protection pacing sequence. In a specific embodiment,postconditioning sequence initiator 338 cancels the initiation of apostconditioning sequence in response to the detection of arrhythmia. Ina specific embodiment, preconditioning sequence initiator 340 holds theinitiation of a prophylactic preconditioning pacing sequence in responseto the detection of arrhythmia unit the arrhythmia is no longerdetected.

In one embodiment, cardiac protection pacing timer 332 terminates orsuspends a cardiac protection pacing sequence in response to thedetection of an arrhythmia that occurs during the cardiac protectionpacing sequence.

FIG. 4 is a block diagram illustrating an embodiment of portions ofcircuits of an implantable system 405 and an external system 415.Implantable system 405 is a specific embodiment of implantable system105. External system 415 is a specific embodiment of external system115.

Implantable system 405 includes lead system 108, one or more sensors409, and implantable medical device 410. Sensor(s) 409 includeselectrodes, accelerometer(s), pressure sensor(s), and/or other sensorsfor sensing one or more signals required for the operation ofimplantable medical device 410, including detection of ischemic events.In various embodiments, sensor(s) 409 are included in an implantablehousing of implantable medical device 410, attached to implantablemedical device 410, coupled to implantable medical device 410 throughwired or wireless connections, and/or incorporated into lead system 108.Implantable medical device 410 is a specific embodiment of implantablemedical device 110 and includes cardiac pacing system 120 (including itsvarious embodiments) and an implant telemetry circuit 450.

External system 415 includes an external telemetry circuit 452, anischemia alert signal receiver 454, and a user interface 456. Externaltelemetry circuit 452 and implant telemetry circuit 450 supportstelemetry link 112, through which directional communication is performedbetween external system 415 and implantable system 405. User interface456 includes a presentation device 458 and a user input device 460.Presentation device 458 includes a display screen. In one embodiment,presentation device 458 further includes a printer and a speaker. Userinput device 460 allows programming of implantable medical device 410,including the entry of commands for initiating one or more cardiacprotection pacing sequences and/or parameters controlling the deliveryof the cardiac protection pacing therapy. In one embodiment, portions ofpresentation device 458 and user input device 460 are integrated as aninteractive screen. Ischemia alert signal receiver 454 receives theischemia alert signal produced by ischemia detector 224 and transmittedto external system 415 via telemetry link 112 and, in response, causespresentation device 458 to produce an alarm signal and/or a warningmessage for the patient and/or a physician or caregiver.

In one embodiment, external system 415 includes a programmer. In anotherembodiment, external system 415 includes a patient management system asdiscussed below with reference to FIG. 5.

FIG. 5 is a block diagram illustrating an embodiment of an externalsystem 515, which is a specific embodiment of external system 415. Asillustrated in FIG. 5, external system 415 is a patient managementsystem including an external device 562, a telecommunication network564, and a remote device 570. External device 562 is placed within thevicinity of an implantable medical device and includes externaltelemetry system 452 to communicate with the implantable medical devicevia telemetry link 112. Remote device 570 is in one or more remotelocations and communicates with external device 562 through network 564,thus allowing a physician or other caregiver to monitor and treat apatient from a distant location and/or allowing access to varioustreatment resources from the one or more remote locations. In oneembodiment, as illustrated in FIG. 5, remote device 570 includes userinterface 456. This allows the user to initiate and/or adjust thecardiac protection pacing therapy in response to the alarm signal and/orwarning message associated with the ischemia alert signal.

FIG. 6 is a flow chart illustrating an embodiment of a method fordelivering pacing pulses for cardiac protection against tissue damageassociated with ischemic events. In one embodiment, the method isperformed by system 100.

One or more signals indicative of an ischemic event are sensed at 600.The ischemic event is detected from the one or more signals at 610. Inresponse to the detection of the ischemic event, one or more cardiacprotection pacing sequences are initiated at 620. The one or morecardiac protection pacing sequences each include alternating pacing andnon-pacing periods. The pacing periods each have a pacing durationduring which a plurality of pacing pulses is delivered. The non-pacingperiods each having a non-pacing duration during which no pacing pulseis delivered. The plurality of pacing pulses is delivered during each ofthe pacing periods at 630.

FIG. 7 is a flow chart illustrating a specific embodiment of the methodfor delivering pacing pulses for cardiac protection that is discussedwith reference to FIG. 6. In one embodiment, the method is performed bysystem 100.

One or more signals indicative of an ischemic event are sensed at 700.The one or more signals are selected from surface ECG signals or othersurface biopotential signals indicative of cardiac activities, wirelessECG signals, electrogram signals, impedance signals, heart soundsignals, pressure signals, acceleration signals, signals representativeof HRV parameters, and/or any other signals having characteristicsallowing detection of ischemic events.

The ischemic event is detected from the one or more signals at 710, byrunning an automatic ischemia detection algorithm. In one embodiment, anischemia alert signal is produced to indicate the detection of theischemic event to the patient and/or a physician or other caregiver.

In response to the detection of the ischemic event, cardiac protectionpacing sequences are initiated and timed at 720. In one embodiment, apacing mode is switched from a chronic pacing mode to a temporary pacingmode when a cardiac protection pacing sequence is initiated and switchedback from the temporary pacing mode to the chronic pacing mode when thecardiac protection pacing sequence is completed. The pacing modedetermines whether and how pacing pulses are delivered before, during,and after the cardiac protection pacing sequence. To trigger the heart'sintrinsic protective mechanism against tissue damage associated withischemia, the temporary pacing mode is substantially different from thechronic pacing mode. In one embodiment, one or more cardiac protectionpacing sequences are also initiated in response to user commands.

The cardiac protection pacing sequences include at least onepostconditioning sequence and a plurality of prophylacticpreconditioning sequences. In response to the detection of the ischemicevent, postconditioning sequence is initiated at 722. In one embodiment,the postconditioning sequence is initiated when the end of the ischemicevent is detected. In a specific embodiment, the end of the ischemicevent is detected when the ischemic event is no longer detected. In aspecific embodiment, the postconditioning pacing sequence is initiatedwhen a post-ischemia time interval expires. The post-ischemia timeinterval starts at the end of the ischemic event and ends after apredicted reperfusion period following the ischemic event has started.In another embodiment, the postconditioning sequence is initiated inresponse to a postconditioning command issued by a user. After beinginitiated, the postconditioning sequence including alternatingpostconditioning pacing and non-pacing periods is timed at 724. Thepostconditioning pacing periods each have a postconditioning pacingduration during which a plurality of pacing pulses is delivered. Thepostconditioning non-pacing periods each have a postconditioningnon-pacing duration during which no pacing pulse is delivered. After thepostconditioning sequence is completed, the prophylactic preconditioningsequences are initiated, one at a time, at 726. In one embodiment, theprophylactic preconditioning pacing sequences are initiated on aperiodic basis with a predetermined period. In another embodiment, theprophylactic preconditioning pacing sequences are initiated according toa preconditioning schedule programmed by the user. In anotherembodiment, the prophylactic preconditioning pacing sequences areinitiated in response to one or more preconditioning commands issued bythe user. After being initiated, each of the prophylacticpreconditioning pacing sequences including alternating preconditioningpacing and non-pacing periods is timed at 728. The preconditioningpacing periods each have a preconditioning pacing duration during whicha plurality of pacing pulses is delivered. The preconditioningnon-pacing periods each have a preconditioning non-pacing durationduring which no pacing pulse is delivered. In one embodiment,predetermined type arrhythmias are detected. The one or more cardiacprotection pacing sequences are suspended in response to the detectionof the arrhythmia.

The plurality of pacing pulses is delivered during each of the pacingperiods of the cardiac protection pacing sequences at 730. That includesthe delivery of pacing pulses during the postconditioning pacing periodsof the postconditioning sequence and the delivery of pacing pulsesduring the preconditioning pacing periods of each of the preconditioningsequences.

It is to be understood that the above detailed description is intendedto be illustrative, and not restrictive. Other embodiments will beapparent to those of skill in the art upon reading and understanding theabove description. The scope of the invention should, therefore, bedetermined with reference to the appended claims, along with the fullscope of equivalents to which such claims are entitled.

1. A cardiac pacing system, comprising: a sensing circuit to sense one or more signals indicative of an ischemic event; an ischemia detector, coupled to the sensing circuit, to detect the ischemic event from the one or more signals; a pulse output circuit to deliver pacing pulses; and a control circuit, coupled to the ischemia detector and the pulse output circuit, to control the delivery of the pacing pulses, the control circuit including: a cardiac protection pacing sequence initiator adapted to initiate one or more cardiac protection pacing sequences in response to the detection of the ischemic event, the one or more cardiac protection pacing sequences each including alternating pacing and non-pacing periods, the pacing periods each having a pacing duration during which a plurality of the pacing pulses is delivered, the non-pacing periods each having a non-pacing duration during which none of the pacing pulses is delivered; and a cardiac protection pacing timer adapted to time the one or more cardiac protection pacing sequences.
 2. The system of claim 1, wherein the control circuit comprises a pacing mode switch adapted to switch a pacing mode from a chronic pacing mode to a temporary pacing mode when one of the one or more cardiac protection pacing sequence is initiated and to switch the pacing mode from the temporary pacing mode to the chronic pacing mode when the one of the one or more cardiac protection pacing sequence is completed, the temporary pacing mode being substantially different from the chronic pacing mode.
 3. The system of claim 1, wherein the cardiac protection pacing sequence initiator comprises a postconditioning sequence initiator adapted to initiate at least one postconditioning sequence in response to the detection of the ischemic event, the postconditioning sequence being one of the one or more cardiac protection pacing sequences.
 4. The system of claim 3, wherein the postconditioning sequence initiator is adapted to initiate the at least one postconditioning sequence after an end of the ischemic event is detected by the ischemia detector.
 5. The system of claim 4, wherein the postconditioning sequence initiator is adapted to initiate the at least one postconditioning pacing sequence when a post-ischemia time interval expires, the post-ischemia time interval starting when the end of the ischemic event is detected by the ischemia detector.
 6. The system of claim 5, wherein the cardiac protection pacing sequence initiator comprises a preconditioning sequence initiator adapted to initiate a plurality of preconditioning sequences in response to the detection of the ischemic event, the preconditioning sequences each being one of the one or more cardiac protection pacing sequences.
 7. The system of claim 6, wherein the preconditioning sequence initiator is adapted to initiate the prophylactic preconditioning sequences on a periodic basis using a predetermined period.
 8. The system of claim 6, wherein the preconditioning sequence initiator is adapted to initiate the prophylactic preconditioning sequences in response to one or more preconditioning commands.
 9. The system of claim 1, wherein the control circuit is adapted to detect an arrhythmia and to suspend the one or more cardiac protection pacing sequences in response to the detection of the arrhythmia.
 10. The system of claim 1, wherein the sensing circuit comprises a cardiac sensing circuit to sense one or more cardiac signals, and the ischemia detector is adapted to detect the ischemic event from the one or more cardiac signals.
 11. The system of claim 10, further comprising one or more surface electrodes coupled to the cardiac sensing circuit and configured to sense one or more surface biopotential signals indicative of cardiac activities as the one or more cardiac signals.
 12. The system of claim 10, further comprising one or more implantable electrodes coupled to the cardiac sensing circuit and configured for subcutaneous placement to sense one or more subcutaneous electrocardiogram signals as the one or more cardiac signals.
 13. The system of claim 10, further comprising one or more implantable electrodes coupled to the cardiac sensing circuit and configured for endocardial or epicardial placement to sense one or more electrogram signals as the one or more cardiac signals.
 14. The system of claim 1, wherein the sensing circuit comprises an impedance sensing circuit to sense an impedance signal indicative of a cardiac impedance or a transthoracic impedance, and the ischemia detector is adapted to detect the ischemic event from the impedance signal.
 15. The system of claim 1, wherein the sensing circuit comprises a heart sound sensing circuit to sense one or more signals indicative of heart sounds, and the ischemia detector is adapted to detect the ischemic event from the one or more signals indicative of heart sounds.
 16. The system of claim 1, wherein the sensing circuit comprises a pressure sensing circuit to sense one or more pressure signals, and the ischemia detector is adapted to detect the ischemic event from the one or more pressure signals.
 17. The system of claim 1, wherein the sensing circuit comprises a cardiac motion sensing circuit to sense one or more acceleration signals each indicative of regional cardiac wall motion, and the ischemia detector is adapted to detect the ischemic event from the one or more acceleration signals.
 18. The system of claim 1, wherein the sensing circuit comprises a heart rate variability (HRV) sensing circuit to sense HRV and produce an HRV parameter being a measure of the HRV, and the ischemia detector is adapted to detect the ischemic event using the HRV parameter.
 19. The system of claim 1, further comprising: an implantable medical device including at least the ischemia detector, the pulse output circuit, and the control circuit; and an external system communicatively coupled to the implantable medical device.
 20. The system of claim 19, wherein the ischemia detector is adapted to produce an ischemia alert signal indicative of the detection of the ischemic event, and the external system comprises: an ischemia alert signal receiver to receive the ischemia alert signal from the implantable medical device; and a presentation device configured to produce at least one of an alarm signal and a warning message when the ischemia alert signal is received.
 21. The system of claim 20, wherein the external system comprises a user input device to receive one or more pacing commands, and the cardiac protection pacing sequence initiator is adapted to initiate the one or more cardiac protection pacing sequences in response to the detection of the ischemic event and the one or more pacing commands.
 22. A method for delivering pacing pulses, the method comprising: sensing one or more signals indicative of an ischemic event; detecting the ischemic event from the one or more signals; initiating one or more cardiac protection pacing sequences in response to the detection of the ischemic event, the one or more cardiac protection pacing sequences each including alternating pacing and non-pacing periods, the pacing periods each having a pacing duration during which a plurality of pacing pulses is delivered, the non-pacing periods each having a non-pacing duration during which no pacing pulse is delivered; and delivering the plurality of pacing pulses during each of the pacing periods.
 23. The method of claim 22, further comprising switching a pacing mode from a chronic pacing mode to a temporary pacing mode when one of the one or more cardiac protection pacing sequence is initiated and to switch the pacing mode from the temporary pacing mode to the chronic pacing mode when the one of the one or more cardiac protection pacing sequence is completed, the temporary pacing mode substantially different from the chronic pacing mode.
 24. The method of claim 22, wherein the one or more cardiac protection pacing sequences comprises at least one postconditioning sequence, and further comprising initiating the at least one postconditioning sequence after an end of the ischemic event is detected.
 25. The method of claim 24, wherein initiating the at least one postconditioning sequence comprises initiating the at least one postconditioning pacing sequence when a post-ischemia time interval expires, the post-ischemia time interval starting when the end of the ischemic event is detected and is up to approximately 10 minutes.
 26. The method of claim 24, further comprising timing the at least one postconditioning sequence having a postconditioning sequence duration in a range of approximately 30 seconds to 1 hour and including alternating postconditioning pacing and non-pacing periods, the postconditioning pacing periods each having a postconditioning pacing duration in a range of approximately 5 seconds to 10 minutes during which the plurality of pacing pulses is delivered, the postconditioning non-pacing periods each having a postconditioning non-pacing duration in a range of approximately 5 seconds to 10 minutes during which no pacing pulse is delivered.
 27. The method of claim 26, wherein the one or more cardiac protection pacing sequences further comprise a plurality of prophylactic preconditioning sequences, and further comprising initiating the prophylactic preconditioning sequences after the postconditioning sequence is completed.
 28. The method of claim 27, wherein initiating the prophylactic preconditioning sequences comprises initiating the prophylactic preconditioning pacing sequences on a periodic basis using a predetermined period in a range of approximately 24 hours to 72 hours.
 29. The method of claim 27, wherein initiating the prophylactic preconditioning sequences comprises initiating the prophylactic preconditioning pacing sequences in response to one or more preconditioning commands.
 30. The method of claim 27, further comprising timing the plurality of prophylactic preconditioning pacing sequences each having a preconditioning sequence duration in a range of approximately 10 minutes to 1 hour and each including alternating preconditioning pacing and non-pacing periods, the preconditioning pacing periods each having a preconditioning pacing duration in a range of approximately 1 minute to 30 minutes during which the plurality of pacing pulses is delivered, the preconditioning non-pacing periods each having a preconditioning non-pacing duration in a range of approximately 1 minute to 30 minutes during which no pacing pulse is delivered.
 31. The method of claim 22, further comprising: detecting an arrhythmia; and suspending the one or more cardiac protection pacing sequences when the arrhythmia is detected.
 32. The method of claim 22, wherein sensing the one or more signals comprises sensing one or more cardiac signals, and detecting the ischemic event comprises detecting the ischemic event from the one or more cardiac signals.
 33. The method of claim 32, wherein sensing the one or more cardiac signals comprises sensing surface biopotentials using multiple surface electrodes.
 34. The method of claim 32, wherein sensing the one or more cardiac signals comprises sensing one or more subcutaneous electrocardiogram signals using subcutaneously implantable electrodes.
 35. The method of claim 32, wherein sensing the one or more cardiac signals comprises sensing one or more electrogram signals using implantable endocardial or epicardial electrodes.
 36. The method of claim 22, wherein sensing the one or more signals comprises sensing an impedance signal indicative of a cardiac impedance or transthoracic impedance, and detecting the ischemic event comprises detecting the ischemic event from the impedance signal.
 37. The method of claim 22, wherein sensing the one or more signals comprises sensing a signal indicative of heart sounds, and detecting the ischemic event comprises detecting the ischemic event from the signal indicative of heart sounds.
 38. The method of claim 22, wherein sensing the one or more signals comprises sensing a pressure signal indicative of a blood pressure, and detecting the ischemic event comprises detecting the ischemic event from the pressure signal.
 39. The method of claim 22, wherein sensing the one or more signals comprises sensing an acceleration signal indicative of regional cardiac wall motion, and detecting the ischemic event comprises detecting the ischemic event from the acceleration signal.
 40. The method of claim 22, wherein sensing the one or more signals comprises sensing a heart rate variability (HRV) signal indicative of an HRV parameter, and detecting the ischemic event comprises detecting the ischemic event from the HRV signal. 